I owned a 67 BelvedereII Hemi 4 speed car, 100% stock with a half tank of gas it weighed 3880 lbs on the scales at Infinion Raceway.

GTX's had buckets seats (Belvedere had a bench) GTX had two lightweight hood scoops, Belvedere had none. Hemis weigh a tad more than a 440, auto's had 8.75 axles, 4 speeds had Dana 60's, so there's another 50 lbs difference between them. Otherwise a 67 GTX vs Belvedere would be near identical in weight. So there's a good baseline for you to guess from on the 440 GTX.Based on all this I'd guess a 440 auto 67 GTX would weigh in at right around 3,700-3,800lbs.